Neurofibrillary tangles, composed of intracellular aggregates of hyperphosphorylated tau protein are by far the most correlated pathology with clinical symptoms of Alzheimer disease (AD). Emerging evidence suggests that extracellular vesicles (EVs), such as exosomes and microvesicles, transfer pathological tau protein between cells as vehicles, and propagate tau pathology in different brain regions. It is urgently important to find the molecular basis of brain-derived EV, which critically regulates the transport and uptake of pathogenic tau protein between neuronal cells and aggregation of tau protein in recipient neurons. The purpose of the current application is to delineate the effect of P2RX7, a purinergic receptor, on EV- mediated tau propagation. Our preliminary data have shown that suppressing microglial EV secretion by GSK 1482160 compound, a specific inhibitor of the P2RX7, dramatically reduces tau aggregation in CA1 and CA3 pyramidal neuronal cells and dentate granular cells with P301S tauopathy animal model. Interestingly this coalesces with reduction of exosome-specific ?endosomal sorting complexes required for transport? (ESCRT) EV marker, TSG101, in the same hippocampal regions, suggesting the possible EV trafficking from microglia to hippocampal neurons, which may transfer and seeds misfolded tau and accelerate protein aggregation in receiving neurons. Thus, those data indicate the regulatory mechanism by P2RX7 on EV mediated tau propagation and posit the therapeutic potential of the P2RX7 inhibitor for AD or other tauopathy. We hypothesize that P2RX7 critically regulates the transfer of EVs between microglia and neurons in the hippocampal neurons, thereby facilitate spreading misfolded tau. We will validate the effect of GSK1482160 on tau propagation by recapitulating those findings using P2rx7 deletion in P301S tau mice and adeno-associated virus (AAV)-based tau propagation mouse model. In Aim 1, we will determine the effect of systemic deletion of P2rx7 in P301S mouse. The distribution of EV markers and tau pathology in the hippocampal regions will be evaluated and compared with the findings from GSK1482160-administered P301S mice. In Aim 2, we will determine the effect of P2RX7 on secretion and transfer of EV and EV-associated tau and its aggregation potency in vitro. This will determine which cell type is particularly responsible for P2RX7 regulated tau spread into hippocampal neurons. In Aim 3, we will confirm the cell type, which is selected in Aim 2, for the export of EVs into hippocampal neurons by cell type- specific deletion of P2rx7 or Tsg101, an exosome synthesis molecule, and validate if P2RX7-mediated EV secretion are responsible for tau propagation using AAV-based tau propagation mouse model. Successful completion of this study will enhance our understanding of molecules that mediates secretion of EVs from glia to neurons in vitro and in vivo, and identify novel targets for AD.